Distance estimation method based on handheld light field camera

ABSTRACT

A distance estimation method based on a handheld light field camera is disclosed and includes: S1: extracting parameters of the light field camera; S2: setting a reference plane and a calibration point; S3: refocusing a collected light field image on the reference plane, to obtain a distance between a main lens and a microlens array of the light field camera, and recording an imaging diameter of the calibration point on the refocused image; and S4: inputting the parameters of the light field camera, the distance between the main lens and the microlens array, and the imaging diameter of the calibration point on the refocused image to a light propagation mathematical model, and outputting a distance of the calibration point. The present application has high efficiency and relatively high accuracy.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of PCT/CN2017/096573,filed on Aug. 9, 2017. The contents of PCT/CN2017/096573 are all herebyincorporated by reference.

BACKGROUND OF THE APPLICATION Field of the Invention

The present application relates to the fields of computer vision anddigital image processing, and in particular, to a distance estimationmethod based on a handheld light field camera.

Related Arts

Applications of a light field camera in the computer vision fieldattract much attention of researchers. The light field camera recordsposition and direction information of an object by inserting a microlensarray between a main lens and a sensor of a conventional camera. Asingle original light field image shot by using the light field cameranot only can implement digital refocusing, view synthesis, and extendeddepth of field, but also can perform depth estimation on a scene on animage by using related processing algorithms.

Researchers have provided a lot of depth estimation methods for a lightfield image, which are roughly classified into two types: a depthestimation method based on a single clue and a depth estimation methodbased on multi-clue fusion. In the depth estimation method based on asingle clue, a stereo matching principle is mainly used to obtain asingle clue for depth estimation by searching for a corresponding areaof an extracted sub-aperture image and analyzing a correlation thereof.In the depth estimation method based on multi-clue fusion, multipleclues related to a depth are extracted from light field image data andare effectively fused to estimate the depth, for example, two clues,that is, the consistency and the defocus degree of the sub-apertureimage are fused. However, because the baseline of the light field camerais small and the resolution of the sub-aperture image is low, only alow-precision depth image can be obtained by using the foregoing twotypes of algorithms, and the high complexity of the algorithms causeslow efficiency of the depth estimation.

The disclosure of the content of the foregoing background is only usedto help understand the idea and the technical solutions of the presentapplication, but does not necessarily belong to the prior art of thispatent application. When there is no clear evidence indicating that theforegoing content has been disclosed on the application date of thispatent application, the foregoing background shall not be used toevaluate the novelty and the creativity of this application.

SUMMARY OF THE INVENTION

To resolve the foregoing technical problem, the present applicationprovides a distance estimation method based on a handheld light fieldcamera, and has high efficiency and relatively high accuracy.

To achieve the foregoing objective, the present application uses thefollowing technical solutions:

The present application discloses a distance estimation method based ona handheld light field camera, including the following steps:

S1: extracting parameters of a light field camera, including a focallength, a curvature radius, a pupil diameter, and a central thickness ofa main lens of the light field camera, and a focal length of a microlensarray of the light field camera;

S2: setting a reference plane and a calibration point, where thecalibration point is set on an object whose distance needs to beestimated, and obtaining a distance between the reference plane and themain lens;

S3: refocusing a collected light field image on the reference plane, toobtain a distance between the main lens and the microlens array of thelight field camera, and recording an imaging diameter of the calibrationpoint on the refocused image; and

S4: inputting the parameters of the light field camera that areextracted in step S1, the distance between the main lens and themicrolens array that is obtained in step S3, and the recorded imagingdiameter of the calibration point on the refocused image that isrecorded in step S3 to a light propagation mathematical model, andoutputting a distance of the calibration point.

Preferably, the reference plane and the calibration point set in step S2do not obstruct each other, and the calibration point does not overlapwhen being imaged.

Preferably, step S3 specifically includes refocusing the collected lightfield image on the reference plane by using the following formula:

$\begin{matrix}{{{L_{z}\left\lbrack y_{j} \right\rbrack} = {\sum\limits_{i = {- c}}^{c}\; {L\left\lbrack {v_{m - 1 - c + i},y_{j + {a{({c - i})}}}} \right\rbrack}}},{a \in R_{+}},} & (1)\end{matrix}$

where L denotes the light field image, L_(z) denotes the refocused imageon the reference plane z, a denotes a specific value corresponding to afocusing plane of an object space, that is, a specific valuecorresponding to the reference plane z in this step; y={x,y} denotesposition information of the light field image, v={u,v} denotes directioninformation of the light field image, the subscript m denotes the numberof pixels of each microlens in a one-dimensional direction, c=(m−1)/2, iis an integer with a value range of [−c,c], and the subscript j denotescoordinates of the microlens in a vertical direction.

Preferably, the step of obtaining a distance between the main lens andthe microlens array in step S3 specifically includes:

using a ray tracing method to obtain a coordinate calculation formula ofintersections on a plane F_(u):

F _(i) =m _(i) ×f  (2),

where the distance between the intersections on the plane F_(u) is thebaseline of the light field camera, f is the focal length of the mainlens, and m_(i) is the slope of a light ray between a sensor and themain lens of the light field camera;

a calculation formula of the slope k_(i) of a light ray emitted from theobject in an object space is:

$\begin{matrix}{{k_{i} = \frac{y_{j}^{\prime} - F_{i}}{d_{out} - f}},} & (3)\end{matrix}$

where y_(j)′ denotes a vertical coordinate of the object on thereference plane, and d_(out) denotes the distance between the referenceplane and the main lens; and

obtaining, through calculation according to the formula (3), an incidentposition and an emergent position (p′,q′) of the main lens that arereached by the light ray emitted from the object, and obtaining, throughcalculation according to the emergent position (p′,q′) the distanced_(in) between the main lens and the microlens array:

$\begin{matrix}{{d_{in} = \frac{q^{\prime} - y_{j} + {m_{i}p^{\prime}}}{m_{i}}},} & (4)\end{matrix}$

where y_(j) denotes a vertical coordinate of the center of the microlenswhose subscript is j.

Preferably, the light propagation mathematical model in step S4specifically includes a light propagation incident part and a lightpropagation emergent part.

Preferably, a propagation mathematical model of the light propagationincident part specifically includes:

the light ray emitted from the calibration point enters the main lens atan angle φ, where φ meets the relational expression:

$\begin{matrix}{{{\tan \mspace{14mu} \phi} = \frac{D}{2\left( {d_{out}^{\prime} - {T\text{/}2} + R - \sqrt{R^{2} - {D^{2}\text{/}4}}} \right)}},} & (5)\end{matrix}$

where d_(out)′ denotes an axial distance between the calibration pointand the center of the main lens, R denotes the curvature radius of themain lens, D denotes the pupil radius of the main lens, T denotes thecentral thickness of the main lens, and the light ray emitted from thecalibration point is refracted after entering the main lens, and thefollowing formula is met:

n ₁ sin ψ=sin(φ+θ₁)  (6),

where n₁ denotes a refractive index of the main lens, ψ denotes arefraction angle, and θ₁ meets:

$\begin{matrix}{{\sin \mspace{14mu} \theta_{1}} = {\frac{D}{2R}.}} & (7)\end{matrix}$

Preferably, a propagation mathematical model of the light propagationemergent part specifically includes:

the light ray emitted from the calibration point reaches the emergentposition (p,q) of the main lens after being refracted in the main lens,and is emergent from the emergent position (p,q), and the followingformula is met:

n ₁ sin(θ₁−ψ+θ₂)=sin ω  (8),

where ω denotes an emergent angle, and θ₂ meets:

$\begin{matrix}{{{\sin \mspace{14mu} \theta_{2}} = \frac{q}{R}},} & (9)\end{matrix}$

there are three imaging manners after the light ray emitted from thecalibration point is emergent from the main lens, which are separatelyfocusing on the back side of the sensor, between the sensor and themicrolens array, and between the microlens array and the main lens,where

when the light ray emitted from the calibration point is focused on theback side of the sensor after being emergent from the main lens, thefollowing formula is met:

$\begin{matrix}{{\frac{D_{1}}{d} \approx \frac{D}{f_{x} + d + d_{in}}},} & (10)\end{matrix}$

where D₁ is the imaging diameter that is of the calibration point on therefocused image and that is recorded in step S3, f_(x) is the focallength of the microlens, d_(in) is the distance that is between the mainlens and the microlens array and that is obtained in step S3, d is thedistance between the calibration point and the sensor on a focusingplane of an image space, and the emergent position (p,q) is on a curvedsurface of the main lens, and the following formulas are met:

$\begin{matrix}{{{\tan \left( {\omega - \theta_{2}} \right)} = {\frac{D_{1}}{2d} = \frac{1}{f_{x} + d + d_{in} - p}}};{and}} & (11) \\{{{\left( {R - {T\text{/}2} + p} \right)^{2} + q^{2}} = R^{2}};} & (12)\end{matrix}$

when the light ray emitted from the calibration point is focused betweenthe sensor and the microlens array or between the microlens array andthe main lens after being emergent from the main lens, the followingformula is met:

$\begin{matrix}{{\frac{D_{1}}{d} \approx \frac{D}{f_{x} - d + d_{in}}},} & (13)\end{matrix}$

where D₁ is the imaging diameter that is of the calibration point on therefocused image and that is recorded in step S3, f_(x) is the focallength of the microlens, d_(in) is the distance that is between the mainlens and the microlens array and that is obtained in step S3, d is thedistance between the calibration point and the sensor on a focusingplane of an image space, and the emergent position (p,q) is on thecurved surface of the main lens, and the following formulas are met:

$\begin{matrix}{{{\tan \left( {\omega - \theta_{2}} \right)} = {\frac{D_{1}}{2d} = \frac{q}{f_{x} - d + d_{in} - p}}};{and}} & (14) \\{{\left( {R - {T\text{/}2} + p} \right)^{2} + q^{2}} = {R^{2}.}} & (15)\end{matrix}$

Compared with the prior art, the beneficial effects of the presentapplication are: In the distance estimation method based on a handheldlight field camera of the present application, a shot light field imageis refocused on a reference plane with a known distance, and therefocused image is equivalent to a light field image obtained byshooting after the light field camera is focused. Because the distanceof the shot object (reference plane) is known, the distance between themain lens of the light field camera and the microlens array may befurther acquired, and all other non-focused objects are equivalent tobeing imaged on the sensor after being shot by the focused light fieldcamera. Therefore, the calibration point is set on the object(non-focused) whose distance needs to be estimated, and the distance ofthe object is estimated by analyzing a relationship between the imagingdiameter of the calibration point on the refocused image and thedistance of the calibration point. In the distance estimation method,absolute distances of all objects can be estimated by means ofrefocusing only once, and the method has high efficiency and greatlyimproves the accuracy of distance estimation, and has a good applicationprospect on industrial distance measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a distance estimation method based on ahandheld light field camera according to a preferred embodiment of thepresent application;

FIG. 2 is a light incident model according to a preferred embodiment ofthe present application;

FIG. 3 is a light emergent model according to a preferred embodiment ofthe present application;

FIG. 4 is an imaging manner of a calibration point according to apreferred embodiment of the present application; and

FIG. 5 is a refocused light tracing model according to a preferredembodiment of the present application.

DETAILED DESCRIPTION OF THE INVENTION

The following further describes the present application with referenceto the accompanying drawings and in combination with preferredimplementations.

As shown in FIG. 1, a preferred embodiment of the present applicationdiscloses a distance estimation method based on a handheld light fieldcamera, including the following steps:

S1: Extract parameters of alight field camera, including a focal length,a curvature radius, a pupil diameter, and a central thickness of a mainlens of the light field camera, and a focal length of a microlens arrayof the light field camera.

The focal length of the main lens and the focal length of the microlensarray are used to obtain a distance between the main lens and themicrolens array, and the curvature radius, the pupil diameter, and thecentral thickness of the main lens, and the focal length of themicrolens array are used in a light propagation mathematical model.

S2: Set a reference plane and a calibration point, where the calibrationpoint is set on an object whose distance needs to be estimated, andobtain a distance between the reference plane and the main lens.

The set reference plane and calibration point do not obstruct eachother, the calibration point does not overlap when being imaged, and thedistance between the reference plane and the main lens is used forrefocusing, and is also used to obtain the distance between the mainlens and the microlens array that exists after refocusing.

S3: Refocus a collected light field image on the reference plane, toobtain a distance between the main lens and the microlens array of thelight field camera, and record an imaging diameter of the calibrationpoint on the refocused image.

(1) The refocusing formula may be expressed as:

$\begin{matrix}{{{L_{z}\left\lbrack y_{j} \right\rbrack} = {\sum\limits_{i = {- c}}^{c}\; {L\left\lbrack {v_{m - 1 - c + i},y_{j + {a{({c - i})}}}} \right\rbrack}}},{a \in R_{+}},} & (1)\end{matrix}$

where L denotes the light field image, L_(z) denotes the refocused imageon the reference plane z, a denotes a specific value corresponding to afocusing plane in an object space, that is, a specific valuecorresponding to the reference plane z in this step; y={x, y} denotesposition information of the light field image, v={u,v} denotes directioninformation of the light field image, the subscript m denotes theresolution of an image of the microlens, that is, the number of pixelsof each microlens in a one-dimensional direction, c=(m−1)/2, i is aninteger with a value range of [−c,c], and the subscript j denotescoordinates in a vertical direction of the microlens, and has the valueranging from 0.

An image obtained after being refocused once is equivalent to a lightfield image obtained by shooting after the light field camera isfocused. In this case, images of other non-focused objects on therefocused image are equivalent to being obtained by using the focusedlight field camera. A plane on which these non-focused objects arelocated is the plane z′ shown in FIG. 4, and an imaging diameter oflight rays emitted from the objects on the plane z′ on the sensor, thatis, an imaging diameter D₁ on the refocused image is recorded.

(2) As shown in FIG. 4 and FIG. 5, because a refocusing plane is the setreference plane (plane z), a distance d_(out) between the plane and amain lens 1 is known. A ray tracing method indicates that the distancebetween intersections on a plane F_(u) is the baseline of the lightfield camera. A coordinate calculation formula of the intersections onthe plane F_(u) is:

F _(i) =m _(i) ×f  (2),

where f is the focal length of the main lens 1, m_(i) is the slope of alight ray between a sensor 3 and the main lens 1; m_(i) may be acquiredas long as the focal length and the diameter of the microlens and thenumber of pixels covered by each microlens are known. A calculationformula of the slope k_(i) of the light ray emitted from the object inthe object space is:

$\begin{matrix}{{k_{i} = \frac{y_{j}^{\prime} - F_{i}}{d_{out} - f}},} & (3)\end{matrix}$

where y_(j)′ denotes a vertical coordinate of the object on the plane z(that is, the reference plane). Further, we may obtain, throughcalculation, an incident position and an emergent position (p′,q′) ofthe main lens 1 that are reached by the light ray emitted from theobject. Therefore, the calculation formula of the distance d_(in)between the main lens 1 and the microlens array 2 is:

$\begin{matrix}{{d_{in} = \frac{q^{\prime} - y_{j} + {m_{i}p^{\prime}}}{m_{i}}},} & (4)\end{matrix}$

where y_(j) denotes a vertical coordinate of the center of the microlenswhose subscript is j.

S4: Input the parameters of the light field camera that are extracted instep S1, the distance between the main lens and the microlens array thatis obtained in step S3, and the recorded imaging diameter of thecalibration point on the refocused image that is recorded in step S3 toa light propagation mathematical model, and output a distance of thecalibration point.

S41: Divide the light propagation mathematical model into two parts: alight propagation incident part and a light propagation emergent part.

(1) The light propagation incident part: As shown in FIG. 2, the lightray emitted from the calibration point enters the main lens at an angleφ, where φ meets the relational expression:

$\begin{matrix}{{{\tan \mspace{14mu} \phi} = \frac{D}{2\left( {d_{out}^{\prime} - {T\text{/}2} + R - \sqrt{R^{2} - {D^{2}\text{/}4}}} \right)}},} & (5)\end{matrix}$

where d_(out)′ denotes an axial distance between the calibration pointand the center of the main lens of the light field camera; and R, D, andT are the parameters of the main lens, which separately denote thecurvature radius, the pupil diameter, and the central thickness of themain lens. The light ray is refracted after entering the main lens, anda refraction formula is used to obtain:

n ₁ sin ψ=sin(φ+θ₁)  (6),

where n₁ denotes a refractive index of the main lens, ψ is a refractionangle, and θ₁ meets:

$\begin{matrix}{{\sin \mspace{14mu} \theta_{1}} = {\frac{D}{2R}.}} & (7)\end{matrix}$

(2) The light propagation emergent part: As shown in FIG. 3, the lightray reaches the position (p,q) of the main lens after being refracted inthe main lens, and is then emergent from the position (p,q), and therefraction formula is used again to obtain:

n ₁ sin(θ₁−ψ+θ₂)=sin ω  (8),

where ω is an emergent angle, and θ₂ meets:

$\begin{matrix}{{\sin \mspace{14mu} \theta_{2}} = {\frac{q}{R}.}} & (9)\end{matrix}$

S42: There are three imaging manners after the light ray is emergent, asthe three light rays 4A, 4B, and 4C shown in FIG. 4, which arerespectively focused on the back side of the sensor 3 (4A), between thesensor 3 and the microlens array 2 (4B), and between the microlens array2 and the main lens 1 (4C).

When the light ray is focused on the back side of the sensor 3, that is,in the imaging situation of the light 4A, a geometrical relationshipamong the main lens 1, the microlens array 2, and the sensor 3 isanalyzed, and approximation is performed by using a similar triangle, toobtain:

$\begin{matrix}{{\frac{D_{1}}{d} \approx \frac{D}{f_{x} + d + d_{in}}},} & (10)\end{matrix}$

where D₁ is the imaging diameter that is of the calibration point andthat is recorded in step S3; f_(x) is the focal length of the microlens;d_(in) is the distance between the main lens 1 and the microlens array2; d is the distance between the calibration point and the sensor on afocusing plane of an image space. The emergent position (p,q) of thelight is on a curved surface of the main lens, and therefore meets thefollowing relational expressions:

$\begin{matrix}{{{\tan \left( {\omega - \theta_{2}} \right)} = {\frac{D_{1}}{2d} = \frac{q}{f_{x} + d + d_{in} - p}}};{and}} & (11) \\{{\left( {R - {T\text{/}2} + p} \right)^{2} + q^{2}} = {R^{2}.}} & (12)\end{matrix}$

When the light ray is focused between the sensor 3 and the microlensarray 2 or between the microlens array 2 and the main lens 1, that is,in the two imaging situations of the lights 4B and 4C, approximation isalso performed by using a similar triangle, to obtain:

$\begin{matrix}{{\frac{D_{1}}{d} \approx \frac{D}{f_{x} - d + d_{in}}};} & (13) \\{{{\tan \left( {\omega - \theta_{2}} \right)} = {\frac{D_{1}}{2d} = \frac{q}{f_{x} - d + d_{in} - p}}};{and}} & (14) \\{{\left( {R - {T\text{/}2} + p} \right)^{2} + q^{2}} = {R^{2}.}} & (15)\end{matrix}$

S43: Input the distance d_(in) between the main lens of the light fieldcamera and the microlens array, and the imaging diameter D₁ of thecalibration point that exist after refocusing.

When the light ray is focused on the back side of the sensor 3, that is,in the imaging situation of the light 4A, the formula (10) may be usedto approximately calculate d:

$\begin{matrix}{d \approx {\frac{\left( {f_{x} + d_{in}} \right)D_{1}}{D - D_{1}}.}} & (16)\end{matrix}$

The calculated d is substituted into the formula (11), and p and q arecalculated in combination with the formula (12). q is substituted intothe formula (9) to obtain θ₂ through calculation:

$\begin{matrix}{\theta_{2} = {{\arcsin \left( \frac{q}{R} \right)}.}} & (17)\end{matrix}$

Then, the obtained θ₂ is substituted into the formula (11) to obtain ωthrough calculation:

$\begin{matrix}{\omega = {{{\arctan \left( \frac{D_{1}}{2d} \right)} + \theta_{2}} = {{\arctan \left( \frac{D_{1}}{2d} \right)} + {{\arcsin \left( \frac{q}{R} \right)}.}}}} & (18)\end{matrix}$

Then, the formulas (7), (8), and (6) are used to sequentially obtain theangles θ₁, ψ, and φ:

$\begin{matrix}{{\theta_{1} = {\arcsin \left( \frac{D}{2R} \right)}};} & (19) \\{{\psi = {{\arcsin \left( \frac{D}{2R} \right)} + {\arcsin \left( \frac{q}{R} \right)} - {\arcsin \left( {{\sin (\omega)}\text{/}n_{1}} \right)}}};{and}} & (20) \\{\phi = {{\arcsin \left( {n_{1}{\sin (\psi)}} \right)} - {{\arcsin \left( \frac{D}{2R} \right)}.}}} & (21)\end{matrix}$

Finally, the formula (5) is used to calculate an absolute distanced_(out)′ of the calibration point:

$\begin{matrix}{d_{out}^{\prime} = {\frac{D}{2\mspace{14mu} {\tan (\phi)}} + \sqrt{R^{2} + {D^{2}\text{/}4}} - R + {T\text{/}2.}}} & (22)\end{matrix}$

When the light ray is focused between the sensor 3 and the microlensarray 2 or between the microlens array 2 and the main lens 1, that is,in the two imaging situations of the lights 4B and 4C, the formula (13)may be used to approximately calculate d:

$\begin{matrix}{d \approx {\frac{\left( {f_{x} + d_{in}} \right)D_{1}}{D + D_{1}}.}} & (23)\end{matrix}$

The calculated d is substituted into the formula (14), and p and q arecalculated in combination with the formula (15). Then, solution formulasof all angles are the same as the formulas (17) to (21), and finally,the formula (5) is used to calculate the absolute distance d_(out)′ ofthe calibration point.

In the distance estimation method based on a handheld light field cameraof the preferred embodiments of the present application, first, a shotlight field image is refocused on a reference plane with a knowndistance, and the focused image is equivalent to a light field imageobtained by shooting after the light field camera is focused. Becausethe distance of the shot object (reference plane) is known, a distancebetween the main lens of the light field camera and the microlens arraymay be further acquired, and all other non-focused objects areequivalent to being imaged on the sensor after being shot by the focusedlight field camera. Therefore, the calibration point is set on theobject (non-focused) whose distance needs to be estimated, and thedistance of the object is estimated by analyzing a relationship betweenthe imaging diameter of the calibration point on the refocused image andthe distance of the calibration point. A specific implementation stepis: extracting parameters of the light field camera, including a focallength, a curvature radius, a pupil diameter, and a central thickness ofa main lens, and a focal length of a microlens; setting a referenceplane and a calibration point, where the calibration point is set on anobject whose distance needs to be estimated, and obtaining a distancebetween the reference plane and the main lens of the light field camera;refocusing a collected light field image on the reference plane, toobtain a distance between the main lens and a microlens array of thelight field camera, and recording an imaging diameter of the calibrationpoint on the refocused image; providing a light propagation mathematicalmodel after analyzing an imaging system of the light field camera; andinputting the parameters of the light field camera, the imagingdiameter, and the obtained distance between the main lens and themicrolens array to the light propagation mathematical model, andoutputting a distance of the calibration point. Because the calibrationpoint is on the object, the estimated distance of the calibration pointis the distance of the object. With the distance estimation method ofthe present application, absolute distances between all objects and themain lens of the light field camera can be estimated by means ofrefocusing once. The method has high efficiency and relatively highaccuracy, and the high efficiency and accuracy provide the method of thepresent application with a bright application prospect on industrialdistance measurement.

The foregoing content is further detailed descriptions of the presentapplication in combination with the specific preferred implementations,and it cannot be regarded that the specific implementations of thepresent application are only limited to these descriptions. A personskilled in the technical field of the present application can still makeseveral equivalent replacements or obvious variations without departingfrom the idea of the present application. The equivalent replacements orobvious variations have same performance or purpose, and shall fallwithin the protection scope of the present application.

What is claimed is:
 1. A distance estimation method based on a handheldlight field camera, comprising the following steps: S1: extractingparameters of alight field camera, comprising a focal length, acurvature radius, a pupil diameter, and a central thickness of a mainlens of the light field camera, and a focal length of a microlens arrayof the light field camera; S2: setting a reference plane and acalibration point, wherein the calibration point is set on an objectwhose distance needs to be estimated, and obtaining a distance betweenthe reference plane and the main lens; S3: refocusing a collected lightfield image on the reference plane, to obtain a distance between themain lens and the microlens array of the light field camera, andrecording an imaging diameter of the calibration point on the refocusedimage; and S4: inputting the parameters of the light field camera thatare extracted in step S1, the distance between the main lens and themicrolens array that is obtained in step S3, and the imaging diameter ofthe calibration point on the refocused image that is recorded in step S3to a light propagation mathematical model, and outputting a distance ofthe calibration point.
 2. The distance estimation method according toclaim 1, wherein the reference plane and the calibration point set instep S2 do not obstruct each other, and the calibration point does notoverlap when being imaged.
 3. The distance estimation method accordingto claim 1, wherein step S3 specifically comprises refocusing thecollected light field image on the reference plane by using thefollowing formula: $\begin{matrix}{{{L_{z}\left\lbrack y_{j} \right\rbrack} = {\sum\limits_{i = {- c}}^{c}\; {L\left\lbrack {v_{m - 1 - c + i},y_{j + {a{({c - i})}}}} \right\rbrack}}},{a \in R_{+}},} & (1)\end{matrix}$ wherein L denotes the light field image, L_(z) denotes therefocused image on the reference plane z, a denotes a specific valuecorresponding to the reference plane z; y={x, y} denotes positioninformation of the light field image, v={u,v} denotes directioninformation of the light field image, the subscript m denotes the numberof pixels of each microlens in a one-dimensional direction, c=(m−1)/2, iis an integer with a value range of [−c,c], and the subscript j denotescoordinates of the microlens in a vertical direction.
 4. The distanceestimation method according to claim 3, wherein the step of obtaining adistance between the main lens and the microlens array in step S3specifically comprises: using a ray tracing method to obtain acoordinate calculation formula of intersections on a plane F:F _(i) =m _(i) ×f  (2), wherein the distance between the intersectionson the plane F_(u) is the baseline of the light field camera, f is thefocal length of the main lens, and m_(i) is the slope of a light raybetween a sensor and the main lens of the light field camera; acalculation formula of the slope k_(i) of a light ray emitted from theobject in an object space is: $\begin{matrix}{{k_{i} = \frac{y_{j}^{\prime} - F_{i}}{d_{out} - f}},} & (3)\end{matrix}$ wherein y_(j)′ denotes a vertical coordinate of the objecton the reference plane, and d_(out) denotes the distance between thereference plane and the main lens; and obtaining, through calculationaccording to the formula (3), an incident position and an emergentposition (p′,q′) of the main lens that are reached by the light rayemitted from the object, and obtaining, through calculation according tothe emergent position (p′,q′), the distance d_(in) between the main lensand the microlens array: $\begin{matrix}{{d_{in} = \frac{q^{\prime} - y_{j} + {m_{i}p^{\prime}}}{m_{i}}},} & (4)\end{matrix}$ wherein y_(j) denotes a vertical coordinate of the centerof the microlens whose subscript is j.
 5. The distance estimation methodaccording to claim 1, wherein the light propagation mathematical modelin step S4 specifically comprises a light propagation incident part anda light propagation emergent part.
 6. The distance estimation methodaccording to claim 5, wherein a propagation mathematical model of thelight propagation incident part specifically comprises: the light rayemitted from the calibration point enters the main lens at an angle φ,wherein φ meets the relational expression: $\begin{matrix}{{{\tan \mspace{14mu} \phi} = \frac{D}{2\left( {d_{out}^{\prime} - {T\text{/}2} + R - \sqrt{R^{2} - {D^{2}\text{/}4}}} \right)}},} & (5)\end{matrix}$ wherein d_(out)′ denotes an axial distance between thecalibration point and the center of the main lens, R denotes thecurvature radius of the main lens, D denotes the pupil radius of themain lens, T denotes the central thickness of the main lens, and thelight ray emitted from the calibration point is refracted after enteringthe main lens, and the following formula is met:n ₁ sin ψ=sin(φ+θ₁)  (6), wherein n₁ denotes a refractive index of themain lens, ψ denotes a refraction angle, and θ₁ meets: $\begin{matrix}{{\sin \mspace{14mu} \theta_{1}} = {\frac{D}{2R}.}} & (7)\end{matrix}$
 7. The distance estimation method according to claim 6,wherein a propagation mathematical model of the light propagationemergent part specifically comprises: the light ray emitted from thecalibration point reaches the emergent position (p,q) of the main lensafter being refracted in the main lens, and is emergent from theemergent position (p,q), and the following formula is met:n ₁ sin(θ₁−ψ+₂)=sin ω  (8) wherein ω denotes an emergent angle, and θ₂meets: $\begin{matrix}{{{\sin \mspace{14mu} \theta_{2}} = \frac{q}{R}};} & (9)\end{matrix}$ there are three imaging manners after the light rayemitted from the calibration point is emergent from the main lens, whichare separately focusing on the back side of the sensor, between thesensor and the microlens array, and between the microlens array and themain lens, wherein when the light ray emitted from the calibration pointis focused on the back side of the sensor after being emergent from themain lens, the following formula is met: $\begin{matrix}{{\frac{D_{1}}{d} \approx \frac{D}{f_{x} + d + d_{in}}},} & (10)\end{matrix}$ wherein D₁ is the imaging diameter that is of thecalibration point on the refocused image and that is recorded in stepS3, f_(x) is the focal length of the microlens, d_(in) is the distancethat is between the main lens and the microlens array and that isobtained in step S3, d is the distance between the calibration point andthe sensor on a focusing plane of an image space, and the emergentposition (p,q) is on a curved surface of the main lens, and thefollowing formulas are met: $\begin{matrix}{{{\tan \left( {\omega - \theta_{2}} \right)} = {\frac{D_{1}}{2d} = \frac{q}{f_{x} + d + d_{in} - p}}};{and}} & (11) \\{{{\left( {R - {T\text{/}2} + p} \right)^{2} + q^{2}} = R^{2}};} & (12)\end{matrix}$ when the light ray emitted from the calibration point isfocused between the sensor and the microlens array or between themicrolens array and the main lens after being emergent from the mainlens, the following formula is met: $\begin{matrix}{{\frac{D_{1}}{d} \approx \frac{D}{f_{x} - d + d_{in}}},} & (13)\end{matrix}$ wherein D₁ is the imaging diameter that is of thecalibration point on the refocused image and that is recorded in stepS3, f_(x) is the focal length of the microlens, d_(in) is the distancethat is between the main lens and the microlens array and that isobtained in step S3, d is the distance between the calibration point andthe sensor on a focusing plane of an image space, and the emergentposition (p,q) is on the curved surface of the main lens, and thefollowing formulas are met: $\begin{matrix}{{{\tan \left( {\omega - \theta_{2}} \right)} = {\frac{D_{1}}{2d} = \frac{q}{f_{x} - d + d_{in} - p}}};{and}} & (14) \\{{\left( {R - {T\text{/}2} + p} \right)^{2} + q^{2}} = {R^{2}.}} & (15)\end{matrix}$